West Nile Virus Workup

Updated: Apr 02, 2018
  • Author: Jess D Salinas, Jr, MD; Chief Editor: Elizabeth A Moberg-Wolff, MD  more...
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Workup

Laboratory Studies

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  • The complete blood count (CBC) may show elevated or normal leukocytes values.

  • In cases of encephalitis, hyponatremia may be present. The complication of syndrome of inappropriate ADH (SIADH) secretion is a possibility.

  • Cerebrospinal fluid (CSF) analysis may reveal elevated protein and increased leukocyte levels, with predominant lymphocytes. [26, 27] Glucose levels are usually normal rather than decreased.

  • Serologic testing to detect immunoglobulin M (IgM) antibodies is currently the best means [10] of diagnosing West Nile virus infection.

    • IgM antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA) has been used to detect IgM for the West Nile virus by using serum or CSF samples. [2, 28]

    • False-positive results may occur because of the close relationship of the West Nile virus to other flaviviruses.

    • In light of this limitation, the plaque reduction neutralization test (PRNT) may help to identify false-positive MAC-ELISA results caused by cross-reactions by other flaviviruses.

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Imaging Studies

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  • In acute disease, computed tomography (CT) scans do not show any evidence of abnormalities.

  • In an estimated one third of infected individuals, magnetic resonance imaging (MRI) scans show notable enhancement in the leptomeninges and periventricular areas.

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Histologic Findings

Autopsy findings in some patients with West Nile virus infection reveal mononuclear inflammation that extensively involves the medulla, with some involvement of the cranial nerve roots. [29] However, these findings are not diagnostic for the infection.

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